/Engine/Plugins/Developer/PluginUtils/Source/PluginUtils/Public/PluginUtils.h
Adds a directory to the list of paths that are recursively searched for plugins, if that directory isn't already under the search paths.
Whether the plugin search path was modified
static bool AddToPluginSearchPathIfNeeded ( const [FString](API\Runtime\Core\Containers\FString) & Dir, bool bRefreshPlugins, bool bUpdateProjectFile )